Systems and methods for source switching and voltage generation

ABSTRACT

System and method for regulating a power conversion system. An example system controller for regulating a power conversion system includes a first controller terminal associated with a first controller voltage and coupled to a first transistor terminal of a first transistor, the first transistor further including a second transistor terminal and a third transistor terminal, the second transistor terminal being coupled to a primary winding of a power conversion system, a second controller terminal associated with a second controller voltage and coupled to the third transistor terminal, and a third controller terminal associated with a third controller voltage. The first controller voltage is equal to a sum of the third controller voltage and a first voltage difference. The second controller voltage is equal to a sum of the third controller voltage and a second voltage difference.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/734,634, filed Jan. 4, 2013, which claims priority to Chinese PatentApplication No. 201210564309.4, filed Dec. 21, 2012, both applicationsbeing incorporated by reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for sourceswitching and/or internal voltage generation. Merely by way of example,the invention has been applied to a power conversion system. But itwould be recognized that the invention has a much broader range ofapplicability.

Conventional switch-mode power supplies often implement gate controlledswitching using high voltage power MOSFETs. But high voltage start-upcircuits for such switch-mode power supplies are usually manufacturedusing an expensive high voltage semiconductor process. In addition, theconventional switch-mode power supplies often suffer from slow start-upand high standby power consumption.

Hence, it is highly desirable to improve switching schemes of a powerconversion system.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for sourceswitching and/or internal voltage generation. Merely by way of example,the invention has been applied to a power conversion system. But itwould be recognized that the invention has a much broader range ofapplicability.

According to one embodiment, a system controller for regulating a powerconversion system includes a first controller terminal associated with afirst controller voltage and coupled to a first transistor terminal of afirst transistor, the first transistor further including a secondtransistor terminal and a third transistor terminal, the secondtransistor terminal being coupled to a primary winding of a powerconversion system, a second controller terminal associated with a secondcontroller voltage and coupled to the third transistor terminal, and athird controller terminal associated with a third controller voltage.The first controller voltage is equal to a sum of the third controllervoltage and a first voltage difference. The second controller voltage isequal to a sum of the third controller voltage and a second voltagedifference. The system controller is configured to, keep the firstvoltage difference constant and change the second voltage difference toturn on or off the first transistor and to affect a primary currentflowing through the primary winding.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal associatedwith a first controller voltage and coupled to a first transistorterminal of a first transistor, the first transistor further including asecond transistor terminal and a third transistor terminal, the secondtransistor terminal being coupled to a primary winding of a powerconversion system, a second controller terminal associated with a secondcontroller voltage and coupled to the third transistor terminal and afirst capacitor terminal of a first capacitor, and a third controllerterminal associated with a third controller voltage. The systemcontroller further includes a second transistor including a fourthtransistor terminal, a fifth transistor terminal and a sixth transistorterminal, the fifth transistor terminal being coupled to the secondcontroller terminal, and a first clamping component including a firstcomponent terminal and a second component terminal, the first componentterminal being coupled to the first controller terminal.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminalassociated with a first controller voltage and coupled to a firsttransistor terminal of a first transistor, the first transistor furtherincluding a second transistor terminal and a third transistor terminal,the second transistor terminal being coupled to a primary winding of apower conversion system, a second controller terminal associated with asecond controller voltage and coupled to the third transistor terminal,the second controller terminal being further coupled to a firstcapacitor terminal of a first capacitor through a diode, and a thirdcontroller terminal associated with a third controller voltage. Thesystem controller further includes a second transistor including afourth transistor terminal, a fifth transistor terminal and a sixthtransistor terminal, the fifth transistor terminal being coupled to thesecond controller terminal, and the diode including an anode terminaland a cathode terminal, the cathode terminal being coupled to the firstcapacitor terminal, the anode terminal being coupled to the secondcontroller terminal. The system controller is configured to charge thefirst capacitor through the diode in response to one or more currentspikes.

According to yet another embodiment, a system controller for regulatinga power conversion system includes, a first controller terminalassociated with a first controller voltage and coupled to a firsttransistor terminal of a first transistor, the first transistor furtherincluding a second transistor terminal and a third transistor terminal,the second transistor terminal being coupled to a primary winding of thepower conversion system, a second controller terminal associated with asecond controller voltage and coupled to the third transistor terminal,and a third controller terminal associated with a third controllervoltage. The system controller further includes a fourth controllerterminal associated with a fourth controller voltage and coupled to afirst capacitor terminal of a capacitor, the capacitor further includinga second capacitor terminal coupled to the third controller terminal, asecond transistor including a fourth transistor terminal, a fifthtransistor terminal and a sixth transistor terminal, the fifthtransistor terminal being coupled to the second controller terminal, anda switch configured to received a control signal and including a firstswitch terminal and a second switch terminal, the first switch terminalcoupled to the second controller terminal, the second switch terminalcoupled to the fourth controller terminal. The system controller isconfigured to close the switch if the second transistor is turned on andif the fourth controller voltage is smaller than a first threshold.

In one embodiment, a system controller for regulating a power conversionsystem includes, a first controller terminal associated with a firstcontroller voltage and coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the third transistor terminalbeing coupled to a primary winding of the power conversion system, asecond transistor including a fourth transistor terminal, a fifthtransistor terminal and a sixth transistor terminal, the sixthtransistor terminal coupled to a first resistor, and a first clampingcomponent coupled to the fourth transistor terminal. The first clampingcomponent is configured to receive a current associated with the firstcontroller voltage, generate a reference voltage based on at leastinformation associated with the current, and bias the fourth transistorterminal to the reference voltage to generate a supple voltage at thefifth transistor terminal.

In another embodiment, a method for regulating a power conversion systemincluding a system controller with a first controller terminal, a secondcontroller terminal and a third controller terminal, includes,generating a first controller voltage associated with the firstcontroller terminal coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the second transistor terminalbeing coupled to a primary winding of the power conversion system,generating a second controller voltage associated with the secondcontroller terminal coupled to the third transistor terminal, andgenerating a third controller voltage associated with the thirdcontroller terminal. The method further includes processing informationassociated with the first controller voltage, the second controllervoltage and the third controller voltage, the first controller voltagebeing equal to a sum of the third controller voltage and a first voltagedifference, the second controller voltage is equal to a sum of the thirdcontroller voltage and a second voltage difference, keeping the firstvoltage difference constant, and changing the second voltage differenceto turn on or off the first transistor to affect a primary currentflowing through the primary winding.

In yet another embodiment, a method for regulating a power conversionsystem including a system controller with a controller terminalincludes, generating a controller voltage associated with the controllerterminal coupled to a first transistor terminal of a first transistor,the first transistor further including a second transistor terminal anda third transistor terminal, the third transistor terminal being coupledto a primary winding of the power conversion system, generating acurrent associated with the controller voltage, biasing a fourthtransistor terminal of a second transistor to a reference voltage basedon at least information associated with the current, the secondtransistor further including a fifth transistor terminal and a sixthtransistor terminal, the sixth transistor terminal being coupled to aresistor, and generating a supply voltage at the fifth transistorterminal based on at least information associated with the referencevoltage.

According to another embodiment, a system controller for regulating apower conversion system includes a controller terminal associated with acontroller voltage and coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the third transistor terminalbeing coupled to a primary winding of the power conversion system, afirst resistor coupled to the controller terminal, and a clampingcomponent coupled to the first resistor. The clamping component isconfigured to receive a current from the first resistor associated withthe controller voltage, generate a reference voltage based on at leastinformation associated with the current, and output the referencevoltage to a voltage regulator.

According to yet another embodiment, a method for regulating a powerconversion system including a system controller with a controllerterminal includes, generating a controller voltage associated with thecontroller terminal coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the third transistor terminalbeing coupled to a primary winding of the power conversion system,generating a current associated with the controller voltage, the currentflowing through a resistor coupled to the controller terminal,generating a reference voltage based on at least information associatedwith the current, and outputting the reference voltage to a voltageregulator.

Many benefits are achieved by way of the present invention overconventional techniques. For example, some embodiments of the presentinvention provide a scheme of source switching using an internaltransistor in a system controller. In another example, certainembodiments of the present invention provide systems and methods forreducing an under-voltage lockout (UVLO) threshold voltage, e.g., closeto an internal supply voltage. In yet another example, some embodimentsof the present invention provide systems and methods for charging acapacitor quickly during a start-up process to provide a supply voltageusing a conduction current of a transistor.

Depending upon embodiment, one or more of these benefits may beachieved. These benefits and various additional objects, features andadvantages of the present invention can be fully appreciated withreference to the detailed description and accompanying drawings thatfollow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram showing a power conversion system withsource switching and/or internal voltage generation according to anembodiment of the present invention.

FIG. 2 is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toan embodiment of the present invention.

FIG. 3(a) is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toanother embodiment of the present invention.

FIG. 3(b) is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toyet another embodiment of the present invention.

FIG. 4 is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toyet another embodiment of the present invention.

FIG. 5 is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toyet another embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for sourceswitching and/or internal voltage generation. Merely by way of example,the invention has been applied to a power conversion system. But itwould be recognized that the invention has a much broader range ofapplicability.

FIG. 1 is a simplified diagram showing a power conversion system withsource switching and/or internal voltage generation according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications.

The power conversion system 100 includes a controller 102, a primarywinding 142, a secondary winding 144, an auxiliary winding 146, a switch122, capacitors 120, 128, 150, 154 and 158, resistors 124, 130, 132, 136and 152, a full wave rectifying bridge including diodes 160, 162, 164and 166, and diodes 126, 148 and 156. The controller 102 includesterminals 104, 110, 112, 114, 116 and 118. For example, the system 100provides power to one or more light emitting diodes. In another example,the switch 122 is a transistor. In yet another example, the switch 122is a field effect transistor (e.g., a metal-oxide-semiconductor fieldeffect transistor), including a terminal 174 (e.g., drain terminal), aterminal 176 (e.g., gate terminal) and a terminal 178 (e.g., sourceterminal).

According to one embodiment, the transistor 122 is turned on and offbased on a difference between a voltage signal 182 at the terminal 176(e.g., gate terminal) and a voltage signal 180 at the terminal 178(e.g., source terminal). In another example, the system 100 performssource switching of the transistor 122 through changing the voltagesignal 180 at the terminal 178 (e.g., source terminal). In yet anotherexample, the system 100 performs source switching of the transistor 122through keeping the voltage signal 182 at the terminal 176 constant andchanging the voltage signal 180 at the terminal 178 (e.g., sourceterminal). In yet another example, the terminal 174 (e.g., drainterminal) of the transistor 122 is connected, directly or indirectly, tothe primary winding 142, and the terminal 176 (e.g., gate terminal) ofthe transistor 122 is connected to the terminal 116 (e.g., terminalGATE). In yet another example, the terminal 178 (e.g., source terminal)of the transistor 122 is connected to the terminal 118 (e.g., terminalSW).

As shown in FIG. 1, the full wave rectifying bridge including the diodes160, 162, 164 and 166 processes an AC input signal from an AC supplycomponent 170, and generates a voltage signal 172 in some embodiments.For example, the voltage signal 182 increases in magnitude in responseto the voltage signal 172 through the resistor 124 and the capacitor120, and eventually reaches a predetermined magnitude. In anotherexample, the voltage signal 182 is fixed at the predetermined magnitude.In yet another example, if the difference between the voltage signal 182and the voltage signal 180 is larger than a threshold, the transistor122 is turned on. In yet another example, a current 184 flows throughthe transistor 122 into the terminal 118 (e.g., terminal SW), and flowsout of the terminal 112 (e.g., terminal VDD) to charge the capacitor 128in order to provide a supply voltage for the controller 102.

In another embodiment, the system 100 performs internal voltagegeneration for the controller 102. For example, when the controller 102begins to operate normally, the charged capacitor 120 provides aninternal current in order to generate an internal supply voltage for thecontroller 102. In another example, the generated internal supplyvoltage is about 5 V. In yet another example, a supply voltage signal198 at the terminal 112 (e.g., terminal VDD) can be as low as theinternal supply voltage.

FIG. 2 is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toan embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The controller 102 includes a voltage clamper 188(e.g., a zener diode), a diode 186, a driver component 190, and a switch192. For example, the switch 192 is a transistor. In another example,the switch 192 is a field effect transistor (e.g., a MOSFET).

As shown in FIG. 2, the driver component 190 affects a voltage signal194 at a terminal 193 (e.g., gate terminal) of the transistor 192 toturn on or off the transistor 192 according to certain embodiments. Forexample, when the transistor 192 is turned off, the transistor 122 isoff. In another example, when the transistor 192 is turned on, a voltage196 at the terminal 110 is approximately equal to the voltage signal 180and the transistor 122 is on if the difference between the voltagesignal 182 and the voltage signal 180 is larger than a threshold. In yetanother example, during the start-up process, the capacitor 120 ischarged in response to the voltage signal 172 and the voltage signal 182increases in magnitude. Once the voltage signal 182 reaches apredetermined magnitude, the voltage clamper 188 clamps (e.g., fixes)the voltage signal 182 at the predetermined magnitude (e.g., a breakdownvoltage of the voltage clamper 188) in some embodiments. For example, itwas clamped by the voltage clamper 188 in some embodiments. For example,the properties of the voltage damper 188 affect the predeterminedmagnitude (e.g., 18 V). In another example, a maximum value of thevoltage signal 180 is equal to a sum of the voltage signal 182 and avoltage drop on the diode 186 in magnitude. In yet another example,during normal operations, the capacitor 120 continues to receiveelectric charges (e.g., from spikes resulting from the switching of thetransistor 122 and the transistor 192) to keep the voltage signal 182constant or substantially constant.

FIG. 3(a) is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toanother embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The controller 102 includes a voltage clamper 202(e.g., a zener diode), diodes 204 and 212, a driver component 206, aswitch 208, an under-voltage lockout and low drop-out (UVLO & LDO)component 210, a resistor 213 and a switch 214. For example, the switch208 is a transistor. In another example, the switch 208 is a fieldeffect transistor (e.g., a MOSFET).

As shown in FIG. 3(a), the driver component 206 affects a voltage signal216 at a terminal 218 (e.g., gate terminal) of the transistor 208 toturn on or off the transistor 208 according to certain embodiments. Forexample, the status of the transistor 122 (e.g., on or off) depends onwhether the transistor 208 is turned on or off. In another example,during the start-up process, the voltage signal 182 increases inmagnitude in response to the voltage signal 172 through the resistor 124and the capacitor 120. Once the voltage signal 182 reaches apredetermined magnitude, the voltage clamper 202 (e.g., a zener diode)clamps (e.g., fixes) the voltage signal 182 at the predeterminedmagnitude (e.g., a breakdown voltage of the voltage clamper 202) in someembodiments. For example, the properties of the voltage clamper 202affect the predetermined magnitude (e.g., 18 V).

In one embodiment, when the difference between the voltage signal 182and the voltage signal 180 is larger than a threshold, the transistor122 begins to conduct a current 1174 which flows through the terminal118 (e.g., terminal SW). In another example, if the switch 214 is closed(e.g., on) in response to a signal 222 (e.g., porB) generated by theUVLO & LDO component 210, the current 1174 flows through the diode 212and the switch 214 to charge the capacitor 128 and a voltage signal 224at the terminal 112 (e.g., terminal VDD) increases in magnitude. In yetanother example, when the voltage signal 224 exceeds a firstpredetermined threshold voltage (e.g., an upper threshold) in magnitude,the UVLO & LDO component 210 changes the signal 222 to open (e.g., toturn off) the switch 214. In yet another example, if the voltage signal224 drops below a second predetermined threshold voltage (e.g., a lowerthreshold) in magnitude, the UVLO & LDO component 210 changes the signal222 to close (e.g., to turn on) the switch 214 in order to charge thecapacitor 128 again. In yet another example, the current 1174 is limitedby at least the resistor 213 coupled between the terminal 118 (e.g.,terminal SW) and the terminal 112 (e.g., terminal VDD). In anotherexample, a maximum value of the voltage signal 180 is equal to a sum ofthe voltage signal 182 and a voltage drop on the diode 204 in magnitude.In yet another example, the first predetermined threshold voltage isdifferent from or the same as the second predetermined thresholdvoltage. The resistor 213 is omitted in some embodiments.

In another embodiment, the auxiliary winding 146 is removed, and theswitch 214 is always kept on. In yet another embodiment, the auxiliarywinding 146 and the switch 214 are removed, and the diode 212 is coupledbetween the terminal 118 and the terminal 112. For example, without theauxiliary winding 146, the supply voltage of the controller 102 isprovided through the transistor 122. In another example, the switch 214is implemented using a p-channel field effect transistor (e.g., ap-channel metal-oxide-semiconductor field effect transistor).

FIG. 3(b) is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The controller 102 includes a voltageclamper 202 (e.g., a zener diode), diodes 204 and 212, a drivercomponent 206, a transistor 208, an under-voltage lockout and lowdrop-out (UVLO & LDO) component 210, a resistor 213, and a switch 214.In addition, the controller 102 includes a current source 230 and adiode 232. For example, the transistor 208 is a field effect transistor(e.g., a MOSFET).

According to one embodiment, the voltage signal 182 at the terminal 176(e.g., the gate terminal of the transistor 122) is kept no less than apredetermined level. For example, the diode 232 has a forward voltage(e.g., V_(f)). In another example, during normal operation of the powerconversion system 100, the voltage signal 224 at the terminal 112 (e.g.,terminal VDD) is no less than an under-voltage lockout voltage (e.g.,V_(UVLO)). Thus, a minimum of the voltage signal 182 is determined asfollows according to certain embodiments:V _(GATE) ≧V _(UVLO) −V _(f)  (1)where V_(GATE) represents the voltage signal 182. For example, when thevoltage signal 182 is lower in magnitude than the voltage signal 224minus the forward voltage of the diode 232, the capacitor 120 is chargedin response to a current 234 flowing from the terminal 112 (e.g.,terminal VDD) to the terminal 116 (e.g., terminal GATE) through thediode 232.

FIG. 4 is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The controller 102 includes voltageclampers 302 and 332, diodes 304 and 312, a driver component 306,switches 308 and 334, an under-voltage lockout (UVLO) component 310, aswitch 314, and resistors 330 and 336. For example, the switches 308 and334 are transistors. In another example, the switch 308 is a fieldeffect transistor (e.g., a MOSFET). In another example, the switch 334is a field effect transistor (e.g., a MOSFET).

As shown in FIG. 4, the driver component 306 affects a voltage signal316 at a terminal 318 (e.g., gate terminal) of the transistor 308 toturn on or off the transistor 308 according to certain embodiments. Forexample, the status of the transistor 122 (e.g., on or off) depends onwhether the transistor 308 is turned on or off. In another example,during the start-up process, the voltage signal 182 increases inmagnitude in response to the voltage signal 172 through the resistor 124and the capacitor 120. Once the voltage signal 182 reaches apredetermined magnitude, the voltage clamper 302 clamps (e.g., fixes)the voltage signal 182 at the predetermined magnitude (e.g., a breakdownvoltage of the voltage clamper 302) in some embodiments.

In one embodiment, when the difference between the voltage signal 182and the voltage signal 180 is larger than a threshold, the transistor122 begins to conduct a current 1174 which flows through the terminal118 (e.g., terminal SW). In another example, if the switch 314 is closed(e.g., on) in response to a signal 322 (e.g., porB) generated by theUVLO component 310, the current 1174 flows through the diode 312 and theswitch 314 to charge the capacitor 128 and a voltage signal 324 at theterminal 112 (e.g., terminal VDD) increases in magnitude. In yet anotherexample, when the voltage signal 324 exceeds a first predeterminedthreshold voltage (e.g., an upper threshold) in magnitude, the UVLOcomponent 310 changes the signal 322 to open (e.g., to turn off) theswitch 314. In yet another example, if the voltage signal 324 dropsbelow a second predetermined threshold voltage (e.g., a lower threshold)in magnitude, the UVLO component 310 changes the signal 322 to close(e.g., to turn on) the switch 314 in order to charge the capacitor 128again. In yet another example, the first predetermined threshold voltageis different from or the same as the second predetermined thresholdvoltage.

In another embodiment, when the controller 102 begins to operatenormally, and the charged capacitor 120 provides a current 350 whichflows through the resistor 330. For example, a reference voltage signal352 (e.g., V_(ref)) is generated in response to the current 350 flowingfrom the resistor 330 to the voltage clamper 332. In some embodiments,the reference voltage signal 352 is provided to a voltage regulator as areference level. For example, the voltage regulator includes thetransistor 334 which is configured as a source follower. In anotherexample, the reference voltage signal 352 (e.g., V_(ref)) is generatedat a terminal 354 (e.g., gate terminal) of the transistor 334. In yetanother example, once the voltage signal 352 (e.g., V_(ref)) reaches apredetermined magnitude, the voltage clamper 332 clamps (e.g., fixes)the voltage signal 352 at the predetermined magnitude (e.g., a breakdownvoltage of the voltage clamper 332). In yet another example, if thetransistor 334 is turned on, a voltage signal 356 (e.g., AVDD) isgenerated at a terminal 358 of the transistor 334 through the resistor336. In yet another example, the voltage signal 356 (e.g., AVDD) is usedfor providing an internal supply voltage for the controller 102. In yetanother example, the signal 356 (e.g., AVDD) is an internal signal ofthe controller 102, e.g., an internal supply voltage.V _(AVDD) =V _(ref) −V _(th)  (2)where V_(ref) represents the reference voltage signal 352, and V_(th)represents a threshold voltage of the transistor 334.

For example, the breakdown voltage of the voltage clamper 332 (e.g., azener diode) is about 6 V, and a threshold voltage of the transistor 334is about 1 V. The voltage signal 356 is generated to be about 5 V insome embodiments. For example, even if the voltage signal 324 is as lowas about 5 V, the transistor 334 can still generate the voltage signal356 at about 5 V by operating in a linear region. Thus, the secondpredetermined threshold voltage (e.g., the lower threshold) of the UVLOcomponent 310 can be reduced to a low magnitude (e.g., 5 V) in certainembodiments.

In yet another embodiment, during normal operations, the capacitor 120is charged in response to spikes generated at each switching of thetransistor 308 (e.g., M2) through the diode 304 (e.g., D2) in order tokeep the voltage signal 182 constant or substantially constant. Forexample, the resistor 124 has a large resistance in order to reducepower loss. In another example, the spikes are generated mainly when thetransistor 308 is turned off.

FIG. 5 is a simplified diagram showing certain components of thecontroller 102 as part of the power conversion system 100 according toyet another embodiment of the present invention. This diagram is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. The controller 402 includes zenerdiodes 402, 432 and 462, diodes 404 and 412, a driver component 406,transistors 408 and 434, an under-voltage lockout (UVLO) component 410,switches 414, 464, 466 and 468, and resistors 430 and 436. For example,the transistor 408 is a field effect transistor (e.g., a MOSFET). Inanother example, the transistor 434 is a field effect transistor (e.g.,a MOSFET).

As shown in FIG. 5, the driver component 406 affects a voltage signal416 at a terminal 418 (e.g., gate terminal) of the transistor 408 toturn on or off the transistor 408 according to certain embodiments. Forexample, the status of the transistor 122 (e.g., on or off) depends onwhether the transistor 408 is turned on or off. In another example,during the start-up process, the voltage signal 182 increases inmagnitude in response to the voltage signal 172 through the resistor 124and the capacitor 120. Once the voltage signal 182 reaches apredetermined magnitude, it was clamped (e.g., fixed) by at least thezener diode 402 in some embodiments. For example, during the start-upprocess, a voltage signal 424 at the terminal 112 (e.g., terminal VDD)is lower than a first predetermined threshold voltage (e.g., an upperthreshold) in magnitude, and the UVLO component 410 generates a signal422 (e.g., porB) to close (e.g., to turn on) the switches 414 and 464and a signal 470 (e.g., por) to open (e.g., to turn off) the switches466 and 468. In another example, when the signal 422 is at a logic highlevel, the signal 470 is at a logic low level, and when the signal 422is at the logic low level, the signal 470 is at the logic high level.

In one embodiment, when the difference between the voltage signal 182and the voltage signal 180 is larger than a threshold, the transistor122 begins to conduct a current 1174 which flows through the terminal118 (e.g., terminal SW). In another example, if the switch 414 is closed(e.g., on) in response to the signal 422 (e.g., porB), the current 1174flows through the diode 412 and the switch 414 to charge the capacitor128 and the voltage signal 424 at the terminal 112 (e.g., terminal VDD)increases in magnitude. In yet another example, when the voltage signal424 exceeds the first predetermined threshold voltage in magnitude, theUVLO component 410 changes the signal 422 to open (e.g., to turn off)the switch 414. In yet another example, if the voltage signal 424 dropsbelow a second predetermined threshold voltage (e.g., a lower threshold)in magnitude, the UVLO component 410 changes the signal 422 to close(e.g., to turn on) the switch 414 in order to charge the capacitor 128again. In yet another example, if the voltage signal 424 exceeds thefirst predetermined threshold voltage in magnitude, the switch 466 isclosed (e.g., on) in response to the signal 470 generated by the UVLOcomponent 410, and the voltage signal 182 is clamped (e.g., fixed) bythe zener diode 402. In yet another example, if the voltage signal 424drops below the second predetermined threshold voltage in magnitude, theswitch 466 is opened (e.g., off) in response to the signal 470 generatedby the UVLO component 410, and the voltage signal 182 is clamped (e.g.,fixed) by both the zener diode 402 and the zener diode 462. In yetanother example, the first predetermined threshold voltage is differentfrom or the same as the second predetermined threshold voltage.

In another embodiment, when the controller 102 operates normally, if thevoltage signal 424 is larger than the first predetermined thresholdvoltage in magnitude, the switch 468 is closed (e.g., on) in response tothe signal 470 generated by the UVLO component 410 and the switch 464 isopened (e.g., off) in response to the signal 422. In another example,the charged capacitor 120 provides a current 450 which flows through theresistor 430. In yet another example, a reference voltage signal 452(e.g., V_(ref)) is generated in response to the current 450 flowing fromthe resistor 430 to the voltage clamper 432. In some embodiments, thereference voltage signal 452 is provided to a voltage regulator as areference level. For example, the voltage regulator includes thetransistor 434 which is configured as a source follower. In anotherexample, the reference voltage signal 452 is generated at a terminal 454(e.g., gate terminal) of the transistor 434. In yet another example, ifthe transistor 434 is turned on, a voltage signal 456 (e.g., AVDD) isgenerated at a terminal 458 of the transistor 434 through the resistor436. In yet another example, the signal 456 (e.g., AVDD) is an internalsignal of the controller 102, e.g., an internal supply voltage.V _(AVDD) =V _(ref) −V _(th)  (3)where V_(ref) represents the reference voltage signal 452, and V_(th)represents a threshold voltage of the transistor 434.

According to another embodiment, a system controller for regulating apower conversion system includes a first controller terminal associatedwith a first controller voltage and coupled to a first transistorterminal of a first transistor, the first transistor further including asecond transistor terminal and a third transistor terminal, the secondtransistor terminal being coupled to a primary winding of a powerconversion system, a second controller terminal associated with a secondcontroller voltage and coupled to the third transistor terminal, and athird controller terminal associated with a third controller voltage.The first controller voltage is equal to a sum of the third controllervoltage and a first voltage difference. The second controller voltage isequal to a sum of the third controller voltage and a second voltagedifference. The system controller is configured to, keep the firstvoltage difference constant and change the second voltage difference toturn on or off the first transistor and to affect a primary currentflowing through the primary winding. For example, the system controlleris implemented according to FIG. 1, FIG. 2, FIG. 3(a), FIG. 3(b), FIG.4, and/or FIG. 5.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminalassociated with a first controller voltage and coupled to a firsttransistor terminal of a first transistor, the first transistor furtherincluding a second transistor terminal and a third transistor terminal,the second transistor terminal being coupled to a primary winding of apower conversion system, a second controller terminal associated with asecond controller voltage and coupled to the third transistor terminaland a first capacitor terminal of a first capacitor, and a thirdcontroller terminal associated with a third controller voltage. Thesystem controller further includes a second transistor including afourth transistor terminal, a fifth transistor terminal and a sixthtransistor terminal, the fifth transistor terminal being coupled to thesecond controller terminal, and a first clamping component including afirst component terminal and a second component terminal, the firstcomponent terminal being coupled to the first controller terminal. Forexample, the system controller is implemented according to at least FIG.2, FIG. 3(a), FIG. 3(b), FIG. 4, and/or FIG. 5.

According to yet another embodiment, a system controller for regulatinga power conversion system includes a first controller terminalassociated with a first controller voltage and coupled to a firsttransistor terminal of a first transistor, the first transistor furtherincluding a second transistor terminal and a third transistor terminal,the second transistor terminal being coupled to a primary winding of apower conversion system, a second controller terminal associated with asecond controller voltage and coupled to the third transistor terminal,the second controller terminal being further coupled to a firstcapacitor terminal of a first capacitor through a diode, and a thirdcontroller terminal associated with a third controller voltage. Thesystem controller further includes a second transistor including afourth transistor terminal, a fifth transistor terminal and a sixthtransistor terminal, the fifth transistor terminal being coupled to thesecond controller terminal, and the diode including an anode terminaland a cathode terminal, the cathode terminal being coupled to the firstcapacitor terminal, the anode terminal being coupled to the secondcontroller terminal. The system controller is configured to charge thefirst capacitor through the diode in response to one or more currentspikes. For example, the system controller is implemented according toat least FIG. 2, FIG. 3(a), FIG. 3(b), FIG. 4, and/or FIG. 5.

According to yet another embodiment, a system controller for regulatinga power conversion system includes, a first controller terminalassociated with a first controller voltage and coupled to a firsttransistor terminal of a first transistor, the first transistor furtherincluding a second transistor terminal and a third transistor terminal,the second transistor terminal being coupled to a primary winding of thepower conversion system, a second controller terminal associated with asecond controller voltage and coupled to the third transistor terminal,and a third controller terminal associated with a third controllervoltage. The system controller further includes a fourth controllerterminal associated with a fourth controller voltage and coupled to afirst capacitor terminal of a capacitor, the capacitor further includinga second capacitor terminal coupled to the third controller terminal, asecond transistor including a fourth transistor terminal, a fifthtransistor terminal and a sixth transistor terminal, the fifthtransistor terminal being coupled to the second controller terminal, anda switch configured to received a control signal and including a firstswitch terminal and a second switch terminal, the first switch terminalcoupled to the second controller terminal, the second switch terminalcoupled to the fourth controller terminal. The system controller isconfigured to close the switch if the second transistor is turned on andif the fourth controller voltage is smaller than a first threshold. Forexample, the system controller is implemented according to at least FIG.3(a), FIG. 3(b), FIG. 4, and/or FIG. 5.

In one embodiment, a system controller for regulating a power conversionsystem includes, a first controller terminal associated with a firstcontroller voltage and coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the third transistor terminalbeing coupled to a primary winding of the power conversion system, asecond transistor including a fourth transistor terminal, a fifthtransistor terminal and a sixth transistor terminal, the sixthtransistor terminal coupled to a first resistor, and a first clampingcomponent coupled to the fourth transistor terminal. The first clampingcomponent is configured to receive a current associated with the firstcontroller voltage, generate a reference voltage based on at leastinformation associated with the current, and bias the fourth transistorterminal to the reference voltage to generate a supple voltage at thefifth transistor terminal. For example, the system controller isimplemented according to at least FIG. 4, and/or FIG. 5.

In another embodiment, a method for regulating a power conversion systemincluding a system controller with a first controller terminal, a secondcontroller terminal and a third controller terminal, includes,generating a first controller voltage associated with the firstcontroller terminal coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the second transistor terminalbeing coupled to a primary winding of the power conversion system,generating a second controller voltage associated with the secondcontroller terminal coupled to the third transistor terminal, andgenerating a third controller voltage associated with the thirdcontroller terminal. The method further includes processing informationassociated with the first controller voltage, the second controllervoltage and the third controller voltage, the first controller voltagebeing equal to a sum of the third controller voltage and a first voltagedifference, the second controller voltage is equal to a sum of the thirdcontroller voltage and a second voltage difference, keeping the firstvoltage difference constant, and changing the second voltage differenceto turn on or off the first transistor to affect a primary currentflowing through the primary winding. For example, the method isimplemented according to FIG. 1, FIG. 2, FIG. 3(a), FIG. 3(b), FIG. 4,and/or FIG. 5.

In yet another embodiment, a method for regulating a power conversionsystem including a system controller with a controller terminalincludes, generating a controller voltage associated with the controllerterminal coupled to a first transistor terminal of a first transistor,the first transistor further including a second transistor terminal anda third transistor terminal, the third transistor terminal being coupledto a primary winding of the power conversion system, generating acurrent associated with the controller voltage, biasing a fourthtransistor terminal of a second transistor to a reference voltage basedon at least information associated with the current, the secondtransistor further including a fifth transistor terminal and a sixthtransistor terminal, the sixth transistor terminal being coupled to aresistor, and generating a supply voltage at the fifth transistorterminal based on at least information associated with the referencevoltage. For example, the method is implemented according to at leastFIG. 4, and/or FIG. 5.

According to another embodiment, a system controller for regulating apower conversion system includes a controller terminal associated with acontroller voltage and coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the third transistor terminalbeing coupled to a primary winding of the power conversion system, afirst resistor coupled to the controller terminal, and a clampingcomponent coupled to the first resistor. The clamping component isconfigured to receive a current from the first resistor associated withthe controller voltage, generate a reference voltage based on at leastinformation associated with the current, and output the referencevoltage to a voltage regulator. For example, the system controller isimplemented according to at least FIG. 4, and/or FIG. 5.

According to yet another embodiment, a method for regulating a powerconversion system including a system controller with a controllerterminal includes, generating a controller voltage associated with thecontroller terminal coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the third transistor terminalbeing coupled to a primary winding of the power conversion system,generating a current associated with the controller voltage, the currentflowing through a resistor coupled to the controller terminal,generating a reference voltage based on at least information associatedwith the current, and outputting the reference voltage to a voltageregulator. For example, the method is implemented according to at leastFIG. 4, and/or FIG. 5.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system controller for regulating a powerconversion system, the system controller comprising: a first controllerterminal associated with a first controller voltage and coupled to afirst transistor terminal of a first transistor, the first transistorfurther including a second transistor terminal and a third transistorterminal, the second transistor terminal being coupled to a primarywinding of the power conversion system; a second controller terminalassociated with a second controller voltage and coupled to the thirdtransistor terminal; a third controller terminal associated with a thirdcontroller voltage; a second transistor including a fourth transistorterminal, a fifth transistor terminal and a sixth transistor terminal,the fifth transistor terminal being coupled to the second controllerterminal; and a first clamper including a first clamper terminal and asecond clamper terminal, the first clamper terminal being coupled to thefirst controller terminal; wherein: the second controller voltage isequal to a sum of the third controller voltage and a first voltagedifference; and the second transistor is configured to change the firstvoltage difference to turn on or off the first transistor and to affecta current flowing through the primary winding.
 2. The system controllerof claim 1 wherein: the first controller voltage is equal to a sum ofthe third controller voltage and a second voltage difference; and thefirst clamper is configured to keep the second voltage difference fromexceeding a predetermined threshold.
 3. The system controller of claim1, and further comprising: a second clamper including a third clamperterminal and a fourth clamper terminal; a switch configured to receive asignal and including a first switch terminal and a second switchterminal, the first switch terminal coupled to the second clamperterminal and the third clamper terminal, the second switch terminalcoupled to the fourth clamper terminal; and a fourth controller terminalassociated with a fourth controller voltage and coupled to a firstcapacitor terminal of a capacitor, the capacitor further including asecond capacitor terminal coupled to the third controller terminal;wherein the switch is configured to: in response to the fourthcontroller voltage becoming larger than a first threshold, become closedto short the second clamper; and in response to the fourth controllervoltage becoming lower than a second threshold, become open.
 4. Thesystem controller of claim 3 wherein the second controller terminal iscoupled to the fourth controller terminal through a diode, the diodeincluding an anode terminal and a cathode terminal, the cathode terminalbeing coupled to the fourth controller terminal, the anode terminalbeing coupled to the second controller terminal.
 5. A system controllerfor regulating a power conversion system, the system controllercomprising: a first controller terminal associated with a firstcontroller voltage and coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the second transistor terminalbeing coupled to a primary winding of the power conversion system; asecond controller terminal associated with a second controller voltageand coupled to the third transistor terminal; a third controllerterminal associated with a third controller voltage; a fourth controllerterminal associated with a fourth controller voltage and coupled to afirst capacitor terminal of a first capacitor, the first capacitorfurther including a second capacitor terminal coupled to the thirdcontroller terminal; a second transistor including a fourth transistorterminal, a fifth transistor terminal and a sixth transistor terminal,the fifth transistor terminal being coupled to the second controllerterminal; and a switch configured to receive a signal and including afirst switch terminal and a second switch terminal, the second switchterminal coupled to the fourth controller terminal; wherein the switchis configured to, in response to the fourth controller voltage becomingsmaller than a first threshold, become closed.
 6. The system controllerof claim 5 wherein the switch is further configured to, in response tothe fourth controller voltage becoming larger than a second threshold,become open.
 7. The system controller of claim 5, and furthercomprising: a current source including a first source terminal and asecond source terminal, the first source terminal being coupled to thefourth controller terminal; and a diode including an anode terminal anda cathode terminal, the anode terminal being coupled to the secondsource terminal, the cathode terminal being coupled to the firstcontroller terminal; wherein: the first controller terminal is furthercoupled to a third capacitor terminal of a second capacitor, the secondcapacitor further including a fourth capacitor terminal coupled to thethird controller terminal; and the second capacitor is configured to becharged by a current associated with the current source through thediode in response to the first controller voltage being smaller than asecond threshold.
 8. The system controller of claim 5, and furthercomprising: a clamper coupled to the first controller terminal; wherein:the second controller voltage is equal to a sum of the third controllervoltage and a first voltage difference; and the second transistor isconfigured to change the first voltage difference to turn on or off thefirst transistor and to affect a current flowing through the primarywinding.
 9. The system controller of claim 8 wherein: the firstcontroller voltage is equal to a sum of the third controller voltage anda second voltage difference; and the clamper is configured to keep thesecond voltage difference from exceeding a predetermined threshold. 10.A system controller for regulating a power conversion system, the systemcontroller comprising: a first controller terminal associated with afirst controller voltage and coupled to a first transistor terminal of afirst transistor, the first transistor further including a secondtransistor terminal and a third transistor terminal, the secondtransistor terminal being coupled to a primary winding of the powerconversion system; a second controller terminal associated with a secondcontroller voltage and coupled to the third transistor terminal; a thirdcontroller terminal associated with a third controller voltage andcoupled to a first capacitor terminal of a first capacitor, the firstcapacitor further including a second capacitor terminal; and a firstdiode including a first anode terminal and a first cathode terminal, thefirst cathode terminal being coupled to the first controller terminal;wherein: the first controller terminal is further coupled to a thirdcapacitor terminal of a second capacitor, the second capacitor furtherincluding a fourth capacitor terminal; and the second capacitor isconfigured to be charged by a current flowing from the first diode inresponse to the first controller voltage being smaller than a firstthreshold.
 11. The system controller of claim 10, and furthercomprising: a switch configured to receive a signal and including afirst switch terminal and a second switch terminal, the second switchterminal coupled to the third controller terminal; wherein the switch isconfigured to, in response to the third controller voltage becomingsmaller than a second threshold, become closed.
 12. The systemcontroller of claim 11, and further comprising a second diode includinga second anode terminal and a second cathode terminal, the second anodeterminal being coupled to the second controller terminal, the secondcathode terminal being coupled to the first switch terminal.
 13. Thesystem controller of claim 12 wherein the second anode terminal iscoupled to the second controller terminal through a resistor.
 14. Asystem controller for regulating a power conversion system, the systemcontroller comprising: a first controller terminal associated with afirst controller voltage and coupled to a first transistor terminal of afirst transistor, the first transistor further including a secondtransistor terminal and a third transistor terminal, the secondtransistor terminal being coupled to a primary winding of the powerconversion system; a second transistor including a fourth transistorterminal, a fifth transistor terminal and a sixth transistor terminal,the sixth transistor terminal coupled to a first resistor; and a firstclamper coupled to the fourth transistor terminal; wherein the firstclamper is configured to receive a first current associated with thefirst controller voltage, generate a reference voltage based at least inpart on the first current, and bias the fourth transistor terminal tothe reference voltage to generate a supply voltage at the sixthtransistor terminal.
 15. The system controller of claim 14 wherein thefourth transistor terminal is coupled to the first controller terminalthrough a second resistor.
 16. The system controller of claim 14, andfurther comprising: a second controller terminal associated with asecond controller voltage and coupled to the third transistor terminal;and a third controller terminal associated with a third controllervoltage.
 17. The system controller of claim 16, and further comprising:a second clamper coupled to the first controller terminal; and a thirdtransistor configured to change a first voltage difference to turn on oroff the first transistor and to affect a second current flowing throughthe primary winding; wherein the second controller voltage is equal to asum of the third controller voltage and the first voltage difference.18. The system controller of claim 17 wherein: the first controllervoltage is equal to a sum of the third controller voltage and a secondvoltage difference; and the second clamper is configured to keep thesecond voltage difference from exceeding a predetermined threshold. 19.The system controller of claim 14, and further comprising: a secondcontroller terminal associated with a second controller voltage; a thirdcontroller terminal associated with a third controller voltage andcoupled to a first capacitor terminal of a capacitor, the capacitorfurther including a second capacitor terminal coupled to the secondcontroller terminal; and a first switch configured to receive a firstsignal and including a first switch terminal and a second switchterminal, the first switch terminal coupled to the fourth transistorterminal.
 20. The system controller of claim 19, and further comprising:a second switch configured to receive a second signal and configured to:in response to the third controller voltage becoming larger than a firstthreshold, become closed to conduct the first current flowing to thefirst clamper; and in response to the third controller voltage becomingsmaller than a second threshold, become open.
 21. The system controllerof claim 20 wherein the first switch is further configured to: inresponse to the third controller voltage becoming larger than the firstthreshold, become open; and in response to the third controller voltagebecoming smaller than the second threshold, become closed.
 22. Thesystem controller of claim 14, and further comprising: a secondcontroller terminal associated with a second controller voltage; a thirdcontroller terminal associated with a third controller voltage andcoupled to a first capacitor terminal of a capacitor, the capacitorfurther including a second capacitor terminal coupled to the secondcontroller terminal; and a switch configured to receive a signal andconfigured to: in response to the third controller voltage becominglarger than a first threshold, become closed to conduct the firstcurrent flowing to the first clamper; in response to the thirdcontroller voltage becoming smaller than a second threshold, becomeopen.
 23. The system controller of claim 22 wherein the first thresholdand the second threshold are equal.
 24. The system controller of claim22 wherein the first threshold and the second threshold are not equal.25. The system controller of claim 24 wherein the first threshold islarger than the second threshold.
 26. A system controller for regulatinga power conversion system, the system controller comprising: a firstcontroller terminal associated with a first controller voltage andcoupled to a first transistor terminal of a first transistor, the firsttransistor further including a second transistor terminal and a thirdtransistor terminal, the second transistor terminal being coupled to aprimary winding of the power conversion system; a second controllerterminal associated with a second controller voltage and coupled to afirst capacitor terminal of a capacitor, the capacitor further includinga second capacitor terminal; a second transistor including a fourthtransistor terminal, a fifth transistor terminal and a sixth transistorterminal, the sixth transistor terminal coupled to a resistor; a clampercoupled to the fourth transistor terminal; and a switch configured toreceive a signal and configured to: in response to the second controllervoltage becoming larger than a first threshold, become closed to conducta current flowing to the clamper, the current being associated with thefirst controller voltage; and in response to the second controllervoltage becoming smaller than a second threshold, become open; whereinthe clamper is configured to, in response to receiving the current fromthe switch: generate a reference voltage based at least in part on thecurrent; and bias the fourth transistor terminal to the referencevoltage to generate a supply voltage at the sixth transistor terminal.27. The system controller of claim 26 wherein the first threshold andthe second threshold are equal.
 28. The system controller of claim 26wherein the first threshold and the second threshold are not equal. 29.The system controller of claim 28 wherein the first threshold is largerthan the second threshold.
 30. A method for regulating a powerconversion system, the method comprising: generating a first controllervoltage associated with a first controller terminal, the firstcontroller terminal being coupled to a first transistor terminal of afirst transistor and further coupled to a first capacitor terminal of afirst capacitor, the first transistor further including a secondtransistor terminal and a third transistor terminal, the secondtransistor terminal being coupled to a primary winding of the powerconversion system, the first capacitor further including a secondcapacitor terminal; generating a second controller voltage associatedwith a second controller terminal coupled to the third transistorterminal; biasing a third controller terminal to a third controllervoltage, the third controller terminal being coupled to a thirdcapacitor terminal of a second capacitor, the second capacitor furtherincluding a fourth capacitor terminal; and charging the first capacitorby a current flowing from a first diode in response to the firstcontroller voltage being smaller than a first threshold, the first diodeincluding a first anode terminal and a first cathode terminal, the firstcathode terminal being coupled to the first controller terminal.
 31. Amethod for regulating a power conversion system including a systemcontroller with one or more controller terminals, the method comprising:generating a controller voltage associated with the one or morecontroller terminals coupled to a first transistor terminal of a firsttransistor, the first transistor further including a second transistorterminal and a third transistor terminal, the second transistor terminalbeing coupled to a primary winding of the power conversion system;generating a current associated with the controller voltage; biasing afourth transistor terminal of a second transistor to a reference voltagebased at least in part on the current, the second transistor furtherincluding a fifth transistor terminal and a sixth transistor terminal,the sixth transistor terminal being coupled to a resistor; andgenerating a supply voltage at the sixth transistor terminal based atleast in part on the reference voltage.
 32. A method for regulating apower conversion system including a system controller with one or morecontroller terminals, the method comprising: generating a firstcontroller voltage associated with a first controller terminal coupledto a first transistor terminal of a first transistor, the firsttransistor further including a second transistor terminal and a thirdtransistor terminal, the second transistor terminal being coupled to aprimary winding of the power conversion system; biasing a secondcontroller terminal to a second controller voltage, the secondcontroller terminal being coupled to a first capacitor terminal of acapacitor, the capacitor further including a second capacitor terminal;in response to the second controller voltage becoming larger than afirst threshold, closing a switch to conduct a current flowing to aclamper, the current being associated with the first controller voltage,the clamper being coupled to a fourth transistor terminal of a secondtransistor, the second transistor further including a fifth transistorterminal and a sixth transistor terminal; in response to the secondcontroller voltage becoming smaller than a second threshold, opening theswitch; and in response to receiving the current from the switch,generating a reference voltage based at least in part on the current;and biasing the fourth transistor terminal to the reference voltage togenerate a supply voltage at the sixth transistor terminal.